Systems and methods for battery charging

ABSTRACT

A method of charging a battery includes coupling an electricity network or subnetwork to the battery using inductive power transfer, transferring electrical energy to the battery from the electricity network or subnetwork and varying the inductive power transfer using a controller of the electricity network or subnetwork according to at least one predetermined criteria of the electricity network or subnetwork.

REFERENCE TO RELATED APPLICATIONS

The present disclosure is a Divisional Application of co-pending U.S.patent application Ser. No. 15/371,788 filed on Dec. 7, 2016 which is aDivisional Application of co-pending U.S. patent application Ser. No.14/120,197 filed on May 5, 2014 which is a Divisional Application ofU.S. patent application Ser. No. 12/451,436 filed Jan. 13, 2010 which isbased on and claims benefit from International Application NumberPCT/NZ2008/000103 filed on May 9, 2008 which claims benefit from NewZealand applications 555128 filed May 10, 2007 and 556646 filed July 20,2007, the entire contents of each of which are herein incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an Inductive Power Transfer (IPT) pad,a system, method and means for charging a battery of an electric vehicleusing multiple power sources and an electric vehicle powered by saidbattery. More particularly, the invention relates to charging thebattery for an electric vehicle selectively using a high power sourcefor charging at a high rate or a lower power source for charging at alower rate.

BACKGROUND

In the development of pure electric vehicles (i.e., those powered solelyby electricity as opposed to hybrid vehicles), there are a number ofproblems to be solved before these vehicles can gain widespreadacceptance. These include the limited range compared with moreconventionally fuelled vehicles, the inconvenience of having to rememberto recharge a vehicle (even if it is possible to do so at the user'spremises or home) and the severe restrictions that occur should thevehicle not be charged. These problems have been subjected to greaterconsideration in recent times due to heightened concerns about globalwarming. Pure electric vehicles may have a role to play in reducing theeffects of global warming as they are clearly the lowest polluters ofall vehicle types and are capable of operating with a lower carbon‘footprint’ than vehicles powered by more widespread and conventionalmeans.

Many problems with electric vehicles stem directly from the battery usedto store energy to power the vehicle. Virtually all battery types mustbe charged at a rate that is less than the allowable discharge rate,they have a limited capacity, and their cycle life is not great. Thus,it takes quite a long time to charge a vehicle, the time between chargesis shorter than ideal, and the functionality of the battery declinesrapidly with age.

In use, electric vehicles are however very convenient and make idealshopping baskets and short trip commuter vehicles. Other tasks such asdropping off children at schools and running errands are also wellsuited. If the accumulated distance travelled in a day is within therange of the vehicle, then the battery may be recharged over-night, withservice capable of being resumed the next day. This is an idealscenario. However, if the available range is exceeded or the battery hasnot been sufficiently charged, the driver and passengers may be leftstranded, there will likely be a recovery fee, the battery will need tobe fully charged over a longer period of time than a conventional chargecycle and, when using conventional batteries, these will almostcertainly be degraded such that their available capacity is permanentlyreduced from what it was previously. Opportunity charging can help toeliminate this problem and involves partially charging the vehiclewhenever an opportunity presents itself.

In perhaps a more serious situation where circumstances call for thevehicle to be taken on a long trip, there is little that can be done.Here hybrid vehicles may be a good solution as they can travel greatdistances on fossil fuels and refuel at conventional petrol stations.

For these reasons conventional pure electric vehicles have not met allof the modern requirements for a passenger transport vehicle.

Inductive Power Transfer (IPT) provides a useful alternative to moreconventional charging. A charger using IPT is described in New ZealandPatent Application No. 545664, entitled “Single Phase Power Supply forInductively Coupled Power Transfer Systems” and is incorporated hereinby reference. This charger provides many advantages in that it willoperate from a standard single phase supply typically available in thehome, has an excellent power factor and very low harmonics. As a resultof this, it would be possible to operate with several thousand of theseconnected to a utility network without the quality of supply beingdegraded. Moreover, the use of IPT obviates the need for a user tomanually connect a cable to the battery.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved Inductive PowerTransfer (IPT) pad.

It is an object of the invention to provide means for charging a vehiclewhich mitigates the aforementioned problems associated with conventionalelectric vehicles.

An alternative object of the invention is to provide a system forcharging an electric vehicle.

An alternative object of the invention is to provide a method ofcharging an electric vehicle.

Alternatively, it is an object of the invention to at least provide auseful choice.

According to a first aspect of the invention, there is provided aninductive power transfer (IPT) pad comprising a coil having at least oneturn of a conductor; one or more ferromagnetic slabs; and a shieldmember arranged around both said coil and said ferromagnetic slabs forchannelling electromagnetic flux when in use.

Preferably, the conductor is litz wire.

Preferably, the coil comprises a plurality of turns of wire.

Preferably, the ferromagnetic slabs are monolithic slabs.

Preferably, the ferromagnetic slabs are ferrite slabs.

Preferably, each ferromagnetic slab is arranged in substantially thesame plane.

Preferably, each ferromagnetic slab is arranged such that its lengthextends radially from a common point but spaced apart therefrom.

Preferably, each ferromagnetic slab is spaced apart from adjacent slabsby substantially the same angle.

According to a preferred embodiment, the IPT pad comprises eightferromagnetic slabs each spaced apart from adjacent slabs byapproximately 45°. Other configurations may be selected depending onsystem requirements.

Alternatively, in another embodiment, the IPT pad comprises a pluralityof ferromagnetic slabs whereby a subset of the ferromagnetic slabsextend radially from a common point but are spaced apart therefrom, afurther subset of the ferromagnetic slabs extend radially from adifferent common point but are spaced apart therefrom, and a stillfurther subset of the ferromagnetic slabs are aligned perpendicularly tothe direction of an imaginary straight line connecting the said commonpoints, whereby the still further subset of ferromagnetic slabs arepositioned equidistantly from the imaginary line but spaced equallyalong its length and equally on each side of the imaginary line.

Preferably, the coil is arranged in a plane substantially parallel tothat of the ferromagnetic slabs.

Preferably, the coil is positioned to wind around the common point suchthat it passes each slab at approximately the centre of the length ofeach slab.

Preferably, the IPT pad comprises a substantially rigid backplate.

Preferably, the backplate is substantially planar,

Preferably, the plane of the backplate is substantially parallel to theplanes of the ferromagnetic slabs and the coil, with the plane of theslabs located between the planes of the backplate and the coil.

Preferably, each ferromagnetic slab is spaced apart from the backplateby a thermally conductive and mechanically insulating material so as toallow the transfer of heat there between and protect the slab frommechanical shock. According to one embodiment, each slab may be spacedapart from the backplate using foam or rubber pads. The material makingup the slabs is brittle and such steps serve to prevent cracking in theslabs caused by rapid temperature changes and also due to mechanicalstresses exerted on the IPT pad.

According to preferred embodiments, the backplane is formed from amaterial which substantially inhibits the passage of magnetic fluxtherethrough. In one embodiment, this material is aluminium.

Preferably, the shield member is formed from a strip of material withthe ends thereof joined to form a ring.

Preferably, the shield member is formed from aluminium.

Preferably, the shield member is coupled to the backplane.

Preferably, the IPT pad comprises a member having spaces formed thereinfor holding the ferromagnetic slabs in position and having a channel foraccommodating the coil.

Preferably, the member is formed from a material which does notsignificantly affect magnetic flux. In one embodiment, foam or rubber isused.

Preferably, the member is formed by a moulding process.

Preferably, the IPT pad comprises a cover plate formed from a materialthat is substantially transparent to magnetic flux. In one embodimentthis material is a non-toxic plastic.

According to preferred embodiments, the cover plate and the backplateprovide front and rear walls of a housing for the IPT pad, with sidewalls provided by the shield member, the shield member preferably beingconfigured to extend from the backplate to the cover plate.

The IPT pad according to the first aspect provides for improvedperformance in use by channelling the flow of flux from the chargingpad. More particularly, the backplate and the shield member serve todirect flux upwards from the plane of the backplate with less splay offlux in and parallel to the plane of the backplate. This not onlyimproves the inductive coupling but also reduces the chance that anyundesired objects will be subjected to the induced fields during use. Itis important to note that if this leakage is not controlled, it can leadto damage of such objects. For example, in the case of an electricvehicle, such leakage may result in the wheel bearings eroding.

The IPT pad of the present invention is also beneficial in that it isrelatively slimline compared to more conventional IPT pickups. This isparticularly important where pickup pads are coupled to the underside ofan electric vehicle since it is important that ground clearance ismaintained.

According to a second aspect, there is provided an inductive powertransfer system comprising two inductive power transfer pads, whereinthe two inductive power transfer pads are used in combination, one ofthe pads being used as a pickup pad and the other pad as a charging pad.

Preferably, the charging pad is coupleable to a power supply andinductively transfers power to the pickup pad, which is coupleable to aload, such as a battery.

According to a third aspect, there is provided an apparatus for charginga battery of an electric or a hybrid electric vehicle, the apparatuscomprising first means for selectively coupling the battery to a highpower electrical supply; and second means for selectively coupling thebattery to a lower power electrical supply wherein the second means forcoupling comprises a pickup pad electrically coupled to the battery,wherein power is transferred to the pickup pad from a charging pad byinductive power transfer.

Preferably, the first means for coupling comprises a socket electricallycoupled to the battery, wherein power is transferred by plugging a cableconnected to the high power electrical supply into the socket. Thus,electrical energy may be rapidly transferred to the battery using thefirst means for coupling, resulting in rapid charging.

As would be apparent to one of skill in the art, alternatively, thefirst means for coupling comprises a plug electrically coupled to thebattery, wherein power is transferred by plugging the plug into a socketconnected to the cable connected to the high power electrical supply.

Preferably, the second means for coupling comprises a pickup padaccording to the first aspect of the invention.

The use of IPT avoids the need for a user to plug in a cable foropportunity charging, including when a vehicle is parked overnight.Additionally or alternatively, a second socket may be provided or thefirst socket adapted, if required, so that the battery may be connectedto a lower power supply using a cable. Again, in the alternative, thesecond socket may be substituted by a plug configured to mate with asocket connected to the lower power supply. Such embodiments provide forimproved flexibility in that, where provided and where time permits, thebattery may be charged using IPT. If rapid charging is required and ahigh power supply is available, the battery may be connected thereto.However, there remains the possibility that a battery will requirecharging where neither an IPT charging pad or a high power supply isavailable. A user could, perhaps, put the charging pad inside thevehicle when in transit so that, as required, it could be removed fromthe vehicle, appropriately positioned and used for charging. This ispossible because embodiments of the invention involving IPT preferablywork to widely available household voltages but this is inconvenient.Thus, the second socket may be provided, preferably on an outer surfaceof the vehicle, to enable the battery to be connected, via a cable, to alower power supply, such as via a conventional household socket.According to preferred embodiments, the socket used for coupling to thehigh power supply may also be used to couple to a lower power supply. Itis therefore possible to charge a battery via most household circuits,with only a cable needing to be carried in the vehicle.

Thus, depending on requirements and which types of power supply andforms of transfer are available, a user may selectively couple thebattery to a high power supply or a lower power electrical supply,preferably using IPT for transferring power from the lower power supply.

Preferably, the high power supply has a transfer rating between 10 kWand 500 kW.

Preferably, the lower power supply has a transfer rating between 0.5 kWand 2.5 kW so that it may be provided by conventional household wiring.More preferably, the lower power supply is between 1.0 kW and 2.2 kW.

Use of the word “battery” throughout the specification is not used in alimiting way and may include one or any number of cells or batteries, orsuper capacitors.

Preferably, the apparatus comprises an indication means for indicatingalignment between the charging pad and the pickup pad.

Preferably, the apparatus comprises an indication means for indicatingwhen the battery is being charged.

According to a fourth aspect of the invention, there is provided anelectric vehicle comprising a rechargeable battery and the apparatus ofthe third aspect for charging said battery.

The electric vehicle may be a “pure electric vehicle” in that it may bepowered only by electrical energy. However, the invention is not limitedthereto and may be applied to hybrid vehicles which may be powered byelectrical energy and at least one other energy source, such as acombustible fuel. Thus, references to “electric vehicles” herein includeboth pure electric vehicles and hybrid vehicles having electrical energyas one source of power.

According to a fifth aspect of the invention, there is provided a methodof charging a battery of an electric or a hybrid electric vehicle, themethod comprising selectively coupling the battery to a high powersupply or a lower power supply, wherein said coupling the battery to alower power supply comprises positioning an inductive power transferpickup pad electrically coupled to the battery in close proximity to aninductive power transfer charging pad.

Preferably, the step of connecting the battery to the high power supplycomprises mating a plug with a socket, wherein the plug is associatedwith one of the battery and the high power supply, and the socket isassociated with the other one of the battery and the high power supply.

More preferably, the pickup pad is coupled to the underside of thevehicle and the charging pad is provided on the ground, wherein saidselectively coupling the battery to the lower power supply comprisesdriving the vehicle into a position such that the pickup pad ispositioned above, or operably adjacent to, the charging pad.

Preferably, the charging and pickup pads can be variably distanced fromeach other. The charging pad may be raised and lowered from the groundby a raising and lowering means. Alternatively, the pickup pad may beraised and lowered from the underside of the vehicle by a raising andlowering means.

Preferably, the method comprises indicating alignment between thecharging pad and the pickup pad.

Preferably, the method comprises indicating when the battery is beingcharged.

Placement of an IPT pickup pad on the underside of a vehicle ispreferred for aesthetic reasons, because this arrangement provides nophysical obstacle to those moving around the vehicle while it is beingcharged, and because it is improbable that people or other foreignobjects will be subjected to the induced fields during charging.However, the invention is not limited to such placement. A pickup padmay be located essentially anywhere on the vehicle with the charging padbeing mounted so that IPT transfer is enabled when the vehicle is parkedin position. For example, a pickup pad may be provided on the front orrear surface of the vehicle with the charging pad being mounted on awall in a garage so that they inductively couple when the vehicle isparked. While not preferred due to the requirement for userintervention, the invention does not preclude the mounting of the pickuppad and/or the charging pad on a moveable mounting or armature, whereby,following parking of a vehicle, a user may move one or both of the padsso that IPT transfer is enabled. While having the drawback of requiringgreater user intervention, such embodiments do allow for greatertolerances in the parking position of the vehicle.

According to a sixth aspect, there is provided a system for charging abattery of an electric or a hybrid electric vehicle, the systemcomprising an electricity network or subnetwork having at least onegenerator; cabling for transferring energy generated by the at least onegenerator around the network; IPT coupling means for coupling thenetwork to the battery; and control means for controlling the powertransfer from the at least one generator to the battery.

Preferably, the network is coupled to a plurality of batteries of acorresponding plurality of electric or hybrid electric vehicles.

Any energy source may be used by the generator(s) to generate electricalenergy. However, according to preferred embodiments, a renewable energysource is used. Through use of the control means, it is possible toovercome problems associated with the fluctuable nature of powergenerated from renewable sources and enhance the stability of thenetwork by varying the power supplied to the battery so that the powerdemand on the network better matches the available power. These benefitsare more marked according to embodiments of the system in which thenetwork is coupled to a plurality of batteries of a correspondingplurality of electric or hybrid electric vehicles.

Preferably, the control means is configured to vary the power transferso as to optimise the load factor. Thus, a network controller (e.g. autility company) may vary the power transfer to batteries connected totheir network to better match supply and demand.

According to one embodiment, the batteries in the vehicles are owned bya network controller which operates the network and are leased to theowners of the vehicles.

The system of the sixth aspect preferably comprises at least one IPT padaccording to the first aspect and/or at least one apparatus for chargingaccording to the third aspect and/or at least one electric vehicleaccording to the fourth aspect.

Preferably, the control means is controlled by way of a communicationschannel.

According to a seventh aspect of the invention, there is provided amethod of charging a battery of an electric or a hybrid electricvehicle, the method comprising the steps of coupling the battery to anelectricity network or subnetwork using inductive power transfer;transferring electrical energy to the battery via the network; andvarying the power transfer according to at least one predeterminedcriteria.

Preferably, the at least one predetermined criteria may comprise one ormore of: a time of day; the level of demand on the network; the level ofavailable supply in the network, which is particularly relevant wherethe energy source for the network is fluctuable.

Preferably, the method further comprises the steps of coupling batteriesof a plurality of electric vehicles to the network and selectivelytransferring power to all or a subset thereof.

Preferably, the method further comprises the steps of: couplingbatteries of a plurality of electric vehicles to the network; andselectively transferring power to all batteries or a subset thereof.

Preferably, the method comprises the step of varying the electricitymains frequency to determine the battery load on the network.

According to an eighth aspect of the invention there is provided asystem for supplying power to an electricity network, the systemcomprising: an electricity network or subnetwork having at least onegenerator; a plurality of batteries of a plurality of electric orelectric hybrid vehicles; cabling for transferring energy stored in theplurality of batteries; IPT coupling means for coupling the batteries tothe network; and control means for controlling the power transfer fromthe plurality of batteries to the network.

According to a ninth aspect of the invention there is provided a methodof supplying power to an electricity network, the method comprising thesteps of: coupling a plurality of batteries of a plurality of electricor hybrid electric vehicles to the network using inductive powertransfer; transferring electrical energy to the network from thebattery; and varying the power transfer according to at least onepredetermined criteria.

According to a tenth aspect of the invention there is provided a systemfor controlling load demand in an electricity network, the systemcomprising: an electricity network having at least one generator, thefrequency of power supplied by the network being allowed to vary; atleast one load connected to the network; and control means to monitorthe frequency of power supplied by the network, the control meansincreasing or reducing power consumed by the load dependent on thefrequency.

According to an eleventh aspect of the invention there is provided amethod of controlling load demand on an electricity network, the methodcomprising: allowing the frequency of power supplied by the network tovary; monitoring the frequency of power supplied by the network; andincreasing or reducing the power consumed by the load dependent on thefrequency.

Further aspects of the invention, which should be considered in all itsnovel aspects, will become apparent to those skilled in the art uponreading the following description which provides at least one example ofa practical application of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will be described below by wayof example only and without intending to be limiting with reference tothe following drawings, in which:

FIG. 1 is a perspective view showing a preferred relative positioning ofan IPT charging pad and an electric vehicle during charging;

FIG. 2 is a perspective view of a preferred embodiment of an IPT pad;

FIGS. 3 to 5 are alternative perspective views of the embodiment of theIPT pad of FIG. 2, with portions removed in FIGS. 3 and 5, and portionsshown in ghost outline in FIG. 4 so as to show internal detail;

FIG. 5A is a view of an alternative embodiment of an IPT padconfiguration;

FIG. 5B is a plan view of the alternative embodiment of the IPT pad ofFIG. 5A;

FIG. 6 is a schematic representation of an electric vehicle beingcharged according to an embodiment of the invention; and

FIG. 7 is a schematic representation of an embodiment of a systemaccording to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention provide for a multi-source electric vehiclethat is able to operate in most situations that may occur in terms oftypes, length and frequency of trips. References to “multi-sourceelectric vehicles” are used to refer to electric vehicles embodying orcapable of operating with embodiments of the present invention where thebatteries and/or cells used to power the vehicle may be charged usingvarious electrical power sources. Embodiments of the invention provideall of the advantages of a plug-in electric vehicle in that it can berecharged ‘at home’ overnight but, according to preferred embodiments,it does so without the disadvantage of requiring a cable to be pluggedin. More particularly, according to preferred embodiments, a chargingpad is preferably provided on the floor where the vehicle is usuallyparked, such as in the floor of a user's garage. While the vehicle isparked, the charging pad transfers energy to the vehicle's battery byInductive Power Transfer (IPT) via a pickup provided on the underside ofthe vehicle. With nothing to plug in there is nothing to remember andthe battery will be fully charged dependent only on the time available.

The charging pad provided on the floor is energised by a power supplyand the magnetic field produced thereby couples power into the pickupattached to the vehicle and charges the on-board battery. Power transferrates of up to around 2.2 kW are compatible with household outputs onmost utility networks. The control of this power flow may be achievedusing the technique described in U.S. Pat. No. 5,293,308, which isincorporated herein by reference. Other methods are also within thescope of the invention.

FIG. 1 shows a preferred relative positioning of charging pad 20 andvehicle 10 during charging. The pickup pad (not shown) is preferably ofthe same shape and configuration of charging pad 20 and is positioned onthe underside of vehicle 10 so that it is substantially directly abovecharging pad 20 when vehicle 10 is parked. The magnetic flux produced bycharging pad 20 links the two pads. There is no functional requirementfor the pickup pad to be positioned underneath the vehicle but this ispreferred for aesthetic reasons and relative ease of installation forretrofitted vehicles.

FIGS. 2 to 5 show alternative perspective views of charging pad 20according to preferred embodiments of the invention. More particularly,FIG. 2 shows the outer housing of the pad, FIG. 3 shows the pad with aportion of the outer housing cut away to show interior detail, FIG. 4corresponds to the view of FIG. 3 with exterior features shown assee-through to provide additional detail of the internal arrangement ofthe components, and FIG. 5 shows the pad with the top cover removed.Note that the pickup pad is of the same configuration as charging pad 20and description of charging pad 20 also applies to the pickup pad,except that charging pad 20 is coupled to an electrical supply (e.g. themains electricity supply) and the pickup pad is attached to a load(i.e., the vehicle battery to be charged).

Pads 20 are preferably placed an object formed from a material whichsubstantially limits the passage of magnetic flux, such as a metallicbackplate 21 (which is formed from aluminium in a preferred embodiment)with 8 ferrite bars 22 displaced at 45 degrees with respect to eachother. Bars 22 are held in position by rubbery moulding 23. A coil oflitz wire 27 (see FIG. 5) is linked by the magnetic flux passing throughferrite bars 22. Preferably, the coil of litz wire 27 is located onferrite bars 22 in region 24 of pad 20 so that the coils wind round thegenerally circular body of the pad approximately half way along thelengths of bars 22. Aluminium strip 25 is coupled or formed integral tobackplate 21 to assist in controlling the pattern of the flux generated.Cover 28 is coupled to the top of the main circular body of the pad.Cover 28 is formed from a material, such as PVC, or preferably anon-toxic plastic, which does not obstruct the passage of fluxtherethrough. The particular configuration shown enables the pads to berelatively slim-line which is particularly important for the pickup padwhen retrofitted to existing vehicles so as to maintain groundclearance.

More particularly, backplate 21 and strip 25 are appropriately coupledto work together to direct flux generated by the charging pad throughcover 28 in a generally perpendicular direction to backplate 21, therebyproviding for improved coupling between a charging pad and a pickup padsince there is less leakage caused by the splay of flux in directionsgenerally parallel to backplate 21. Backplate 21 and strip 25 areelectrically connected in one embodiment of the invention.

Mechanical or shock insulating pads 26, preferably formed from foam orrubber, are provided to prevent bars 22 from coming into contact withother components of pad 20. Bars 22 are brittle and thermally sensitive,thus pads 26 are ideally also thermally conductive to keep the bars 22cool. Mechanical insulating pads 26 also limit the transfer ofmechanical stresses to bars 22 caused by knocks or impacts on pad 20 andalso due to vibrations such as those generated when pad 20 is mounted ona vehicle.

Using pads configured as shown in the drawings, with a diameter of 400mm and a thickness of 22 mm, power transfer at rates of up to 2 kW isreadily achievable for lateral misalignments of up to +/−50 mm andvertical separations of 25 mm to 75 mm. Power transfer with even largertolerances is possible but this requires larger pads, increasing thecost. Where a charging pad is provided on a floor to couple with apickup pad on the underside of a vehicle, these tolerances translateinto tolerances for the parking position of the vehicle. Relativelysimple methods may be used to assist a driver in parking in the correctposition. For example, a ball on a string may be suspended from theceiling and aligned with a spot on the windscreen when the vehicle is inthe correct position. Alternatively, a charging indicator may beprovided in the vehicle that lights up when the battery is charging andhence the vehicle is in the correct position. Other alternatives will bereadily apparent to one of skill in the art and all such alternativesare within the scope of the present invention.

According to preferred embodiments involving a transfer rate of up toaround 2 kW, bars 22 preferably have a height of 10 mm, width of 30 mmand length of 120 mm, and coil 27 preferably comprises litz wire having0.2 mm diameter individually insulated wires with 120 strands at 3.77mm² or more. Strip 25 preferably has a thickness of around 4 mm andcover 28 preferably has a thickness of approximately 5 mm. It should benoted that the invention is not limited to these particular values andthe skilled person will be aware that other values may be selecteddepending on the desired operational characteristics.

According to embodiments of the invention, the power pad on the floorunder the vehicle takes the place of a ‘track’ in a more conventionalIPT system and the power pad attached to and under the vehicle is thepickup coil. Using the technique described in the above mentioned NewZealand Patent Application No. 545664, this arrangement of coils allowspower to be passed from the floor power pad to the vehicle power pad athigh efficiency such that the battery on the vehicle may be chargedovernight.

Embodiments of the IPT system make opportunity charging of an electricvehicle possible, not only for a single vehicle in the home, but also,for example, for a fleet of delivery vehicles and the like to allowcontinuous operation on a 24×7 basis given that the work scheduleincludes relatively long times where the vehicle can be parked over thefloor mounted power pad. However, the typical charging rate of 2 kW doesnot overcome the limited range problem of electric vehicles, where thetotal energy demand exceeds the available stored energy.

To address this problem, a high power, plug-in charger may be connectedto the vehicle using a separate high power plug to provide rapidcharging of the battery. Not all battery types are capable of acceptingpowers of the magnitude envisaged but lithium batteries are increasinglycapable of doing this.

As noted above, the power pad intervention-free charger is a home-basedIPT charging system providing a charging power of about 2 kW to staywithin the ratings of conventional household wiring. A typical batteryin an electric vehicle may store 50 kWH of energy or 170 AH(Ampere-Hours) at 300V so that the nominal charging rate is 0.04 C(where C stands for the capacity of the battery in AH). This is aconservative and safe estimate. With a single 12 hour charge, 24 kWH ofenergy may be transferred and if the vehicle operates with an averagepower demand of 10 kW, it will have a range of about 2 hours of drivingor approximately 160 km per day. With a longer charging time this rangecan be doubled by having the vehicle fully charged. On the other hand,embodiments of the high power battery charger may provide power at arate of 10 kW-500 kW for 6 minutes corresponding to a charging rate of10 C. Thus in 6 minutes, the battery is fully charged and the vehicle isset for another 300 km before it needs to be charged again. Note that anelectric power flow of 500 kW is high but is still low compared with theenergy flow rate when pumping petrol or diesel fuel into a tank.

This rapid charging will need to be carefully supervised, as needed forpumping petrol, and is not suitable for home applications for a numberof reasons. Few houses have access to a 500 kW utility network and atthis power level the source of supply would be at a higher voltage thanthe normal distribution network. There is also a degree of hazardinvolved so that a commercially rated facility is required. In contrast,the IPT system is safe and easy to use, making it suitable forinstallation in the home or other places a car may be parked, such as inpublic car parks.

The combination of these technologies provides a vehicle with excellentcharacteristics. On a daily basis it is ideal for short trips, commutingand shopping, allowing relatively low cost travelling for typically 160km/day with minimal maintenance and no queuing for fuel. It may be usedfor longer trips requiring refuelling about every 300 km.

FIGS. 5A and 5B show an alternative embodiment of the charging padconfiguration 20 according to the present invention. In FIGS. 5A and 5Bthe pad 20 is an oval shape in plan. Oval power pads can be constructedby extending the circular power pads and adding identical rectangularsections in the middle. The construction of both power pads is againpreferably identical. In FIG. 5B it is shown that the coil 27 islengthened and a subset of additional ferrite or ferromagnetic bars 22Aare added with similar spacing to that of the subset of bars equivalentto those of the circular power pad described above.

The advantage of this oval-shaped arrangement is that the tolerance ofthe pad to lateral movement (in the x direction shown in FIG. 5A) isimproved over the circular pad. This is advantageous as it is relativelydifficult to adjust the position of a vehicle in the x direction,corresponding to a side to side movement for the vehicle. The toleranceof the pads to pickup movement in the y direction, corresponding to theforward and reverse directions of a vehicle when positioned over thepad, is less that that for the circular pad. However, this is lesscritical when parking a vehicle since it is comparatively much easier tomake adjustments in this direction so as to be optimally positioned overthe pad in the y direction.

The ability to control the spacing between the charging pad and thepickup pad attached to the vehicle is also advantageous. This can beachieved using a variety of methods. For example, the charging pad onthe floor may include means for raising and lowering it from the floorsuch as a jack. The jack may be hand or electrically powered.Alternatively, the pickup pad on the underside of the vehicle mayinclude means for increasing or decreasing its distance from theunderside of the vehicle. Again, this may be a jack or other knownmechanisms.

One of the primary advantages of the system described herein is one ofsafety. An inductive charger means there is no plug connection betweenthe charger and the vehicle, unlike in alternative electric vehiclecharging systems. If a user accidentally drives the vehicle away whilststill connected in a plugged system, the apparatus may be damaged and ahazardous situation may arise through broken current-carrying equipment.In contrast, using an IPT system with no requirement to first safelydisengage any plugs, the vehicle would be able to drive safely away,without fear of damage to the equipment or risk of electricity hazard.Furthermore, in the event of flood, the IPT system can function verysafely without the obvious dangers of alternative plugged systems.

FIG. 6 is a schematic drawing of battery 51 of electric vehicle 10 beingcharged by high power electrical supply 52 via cable 53. Duringopportunity charging, battery 51 is supplied with electricity frompickup 20 via wiring 54. High power electrical supply 52 may comprise ahigh power generator or alternatively merely provides an interface orconduit between a high power electricity network and cable 53. Cable 53is provided with a plug (not shown) which mates with a socket (notshown) provided in vehicle 10. Wiring between the socket and battery 51transfers electricity to battery 51. Preferably, the plug is providedwith a safety housing to prevent access to the electrical contacts. Thesocket may be provided at any point on vehicle 10 with wiring providedbetween the socket and battery 51. Thus, the invention is not limited tothe position of the socket shown in FIG. 6.

FIG. 7 is a schematic representation of a system, generally marked 60,according to an embodiment of the invention. Generator 61 provides highpower electricity to facility 63 which includes high power electricalsupplies 52 of FIG. 6. Two high power electrical supplies 52 are shown.However, as would be apparent to one skilled in the art, the inventionis not limited thereto and facility 63 may include one or any number ofsupplies 52, limited only by the available space and the capacity ofgenerator 61. High power cabling 62 acts as a conduit for the transferof high power electricity to facility 63 and also to transformer 64which reduces the supply to that of a lower power, such as thatconventionally found in homes. Lower power cabling 65 then transferslower power electricity to charging pads 20, preferably provided in thefloor of a user's garage. Whilst single generator 61 is shown, system 60may include a plurality of generators and may include separategenerators for the high power supply and the lower power supply.

An important aspect of electric vehicles is their capital cost. They aretypically more expensive than conventional motor cars due to the highcost of the battery. However, according to embodiments of the invention,the battery and the vehicle may be owned by different parties. Moreparticularly, according to one embodiment of a system and methodaccording to the invention, the battery may be owned by a utilitycompany and leased to an owner of a vehicle. According to suchembodiments, users of electric vehicles are clearly provided with thebenefit of having a reduced capital outlay at the time of purchasing avehicle. However, benefits may also be realised by utility companies andnot only through charges levied for supplying the electricity. Inparticular, through appropriate control of power supplied to the IPTcharging pads, utility companies may level their electric load,particularly overnight-when a large number of batteries for electricvehicles may be charging.

With some modification to the electronics system it is also possible totransfer power in reverse from the battery to the utility. In this wayat times of peak power in the utility, power may be taken from thevehicle battery and used to supply the peak. With a greater number ofvehicles this reverse power may be very large and may avoid powershortages. The total energy may be small as the time that the reversepower flow occurs will likely be short.

There are significant financial advantages to a utility company beingable to have a load factor of 1 and this source-side control of ademand-side load would allow this ideal to be approached, if notreached.

A communications channel may be provided between the controller of thenetwork (typically, the utility company) and the vehicles under chargeso as to enable monitoring of the charging of these vehicles. A simplecell-phone channel may be used for this purpose. As the available powervaries the network controller may vary the battery charging demand tomatch it. This would allow the utility company to operate near theirmaximum power with safety as the electric vehicle load can be varied soquickly. This is similar to but more sophisticated than a ripple controlsystem commonly used to control hot water heating. The essentialdifferences are that partial loads are possible, and the loads can bevaried more quickly and precisely.

The ability to manipulate the demand makes it more readily possible tointegrate highly fluctuable ‘renewable’ sources of energy into powernetworks. The manipulation may alternatively be made by allowing thefrequency of the network or grid to vary in response to variations inthe fluctuable source. Thus, in strong gusts of wind over a whole windfarm the power surge may be such that the mains frequency increases by asmall fraction of 1 Hz. These variations in frequency are measured bythe power supply to the IPT charging pad and used to control the powerpad or track current. In principle, the power transferred is madeproportional to the pad current so that by varying the pad current thecharging load can be matched to the available power. The variation cantake place in as short a period as one cycle of the mains power.

For a large number of battery chargers, say 100,000, the pad currentcould be programmed so that, for example, at 49.5 Hz the pad current iszero, and at a frequency 1 Hz higher the pad current is the full ratedcurrent. If all the chargers were at full demand the charging load wouldvary from 100,000×2 kW=200 MW at a frequency of 50.5 Hz to zero at afrequency of 49.5 Hz. The 49.5 Hz set-point can of course also be variedso that full power occurs at whatever frequency is required. Forexample, if the set point was 49 Hz then full power would be taken at 50Hz or higher. In this manner, high surges in power caused by stronggusts of wind over large wind farms can be compensated for.

On the other hand, in the integration of wind power into a powernetwork, there are also commonly periods where the wind completely‘dies’. In practice, these periods must be covered by having a separatespinning generator of the same power capacity, on standby. Thus, if a200 MW wind farm is to be used then 200 MW of spinning reserve must beconnected to the grid, and under ideal circumstances it provides no realpower at all. This protection is very expensive and in many cases makeswind power uneconomic. According to the present invention, thisprecaution is not required. If the wind ‘dies’ then all the batterycharging load drops as soon as the mains frequency reaches the given setpoint (e.g. 49.5 or 50 Hz). As the vehicles charge they willindividually disengage themselves as soon as their batteries are fullycharged so that the actual load is indeterminate and is not simply thetotal number of vehicles connected. The load could be determined using acommunication channel with each vehicle as discussed above but thiswould take time and a simpler option is available. If the set point wasat 49.5 Hz then all of the connected vehicles that are still chargingwould be at 50% power if the frequency was 50 Hz. If the set point wasthen changed to 49.6 Hz then the charging vehicles would drop to 40% oftheir rated power and the change in power, over the whole country, wouldbe 10% of the connected (total) power sink. In this particular examplethe actual power being taken could be increased by 6 times this change,or reduced by 4 times. In essence, the controllable battery chargingload has been precisely determined.

In these circumstances a very high percentage of wind power and/or otherfluctuable energy sources can now be included into the generation mixwithout standby generators knowing how much power is available if thewind dies, and how much spare sink capacity is available if there is asurge. This is a significant advantage over most wind farm integrationschemes and will allow the percentage of wind power to be increasedabove the presently used 6% commonly in, for example, Ireland andGermany, with zero or minimal standby generators necessary. Otherschemes for achieving this flexibility use huge batteries locally at thewind farm to store surplus power but it is more efficient if the energyis transferred directly to its destination, namely the batteries in thevehicles, since this requires only one battery charging operation.Batteries at wind farms are therefore significantly less efficient ifthe ultimate use of the energy is in electric vehicles.

The financial justifications of the invention are interesting. If atypical battery cost $10,000 it might be leased to the car owner for$40/week plus electricity charges of 12 c/kWH charged on the basis ofwhat has been used. A user doing 300 km per week might use 45 kWH at acost of $5.40 plus the battery lease fee of $40 for a total cost of$45.40 or 15 c/km. Some form of road-user charge would also likely beinvolved or again added to the cost of the electricity. This cost/km isperhaps high but is for very moderate usage and if the distancetravelled is doubled the cost/km is significantly reduced at $50.80 for600 km or 8.5 c/km.

Electricity generated from renewable sources other than wind power (e.g.solar, tidal etc) is also applicable to embodiments of the invention.All of these are not particularly stable and like wind may varyconsiderably over relatively short time scales. For example, measuredrates of change for wind power in New Zealand have been as high as 200MW in 5 minutes from a wind farm with a nominal rating of 200 MW. Thusthe integration of such highly fluctuable sources into an electricitynetwork is a huge advantage. With the source-side control as outlinedthe charging load varies at a rate sufficient to match the fluctuablepower on almost a cycle by cycle basis using small changes in thefrequency of supply, allowing the use of energy that would otherwisesimply be wasted. This energy would be generated at a considerably lowercost than electricity from more conventional sources.

The invention thus allows off-peak power to be used effectively andsafely for electric vehicle charging. It also allows energy generatedfrom renewable sources to be conveniently put to use to charge electricvehicles. Furthermore, the invention allows load demand to becontrolled.

Unless the context clearly requires otherwise, throughout thespecification, the words “comprise”, “comprising”, and the like, are tobe construed in an inclusive sense as opposed to an exclusive orexhaustive sense, that is to say, in the sense of “including, but notlimited to”.

It should be noted that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the invention and withoutdiminishing its attendant advantages. It is therefore intended that suchchanges and modifications be included within the present invention.

The invention claimed is:
 1. A method of charging a battery, the methodcomprising: coupling an electricity network or subnetwork to the batteryusing inductive power transfer; transferring electrical energy to thebattery from the electricity network or subnetwork; and varying theinductive power transfer using a controller of the electricity networkor subnetwork according to at least one predetermined criteria of theelectricity network or subnetwork.
 2. The method as claimed in claim 1,further comprising communicating between the controller of theelectricity network or subnetwork and the battery to enable monitoringof charging of the battery.
 3. The method as claimed in claim 1, whereinthe at least one predetermined criteria comprises at least one of: atime of day; a level of demand on the electricity network or subnetwork;or a level of available supply in the electricity network or subnetwork.4. The method as claimed in claim 1, further comprising: coupling theelectricity network or subnetwork to a plurality of batteries; andselectively transferring power to the plurality of batteries dependenton at least one of a level of demand on the electricity network orsubnetwork, or a level of available supply in the electricity network orsubnetwork.
 5. The method as claimed in claim 4, further comprisingvarying a mains electricity supply frequency of the electricity networkor subnetwork to determine battery load on the electricity network orsubnetwork.
 6. A system for charging a battery, the system comprising: awireless coupler configured to couple an electricity network orsubnetwork to the battery using inductive power transfer; a chargerconfigured to transfer electrical energy to the battery from theelectricity network or subnetwork; and a controller of the electricitynetwork or subnetwork configured to vary the inductive power transferaccording to at least one predetermined criteria of the electricitynetwork or subnetwork.
 7. The system as claimed in claim 6, furthercomprising a communications channel configured to communicate betweenthe controller of the electricity network or subnetwork and the chargerto enable monitoring of the charging of the battery, wherein thecontroller of the electricity network or subnetwork is configured tocommunicate with the charger, via the communications channel, to varythe inductive power transfer via the communications channel.
 8. Thesystem as claimed in claim 6, wherein the controller of the electricitynetwork or subnetwork is configured to vary the inductive power transferaccording to at least one of: a time of day; a level of demand on theelectricity network or subnetwork; or a level of available supply in theelectricity network or subnetwork.
 9. The system as claimed in claim 6,wherein: the electricity network or subnetwork is coupled to a pluralityof batteries; and the controller of the electricity network orsubnetwork is configured to selectively transfer power to the pluralityof batteries dependent on at least one of a level of demand on theelectricity network or subnetwork, or a level of available supply in theelectricity network or subnetwork.
 10. The system as claimed in claim 6,wherein the system comprises: an electricity network or subnetworkhaving at least one generator; and cabling for transferring energy,generated by the at least one generator, around the electricity networkor subnetwork to the wireless coupler; wherein the controller isconfigured to control the inductive power transfer to change the load onthe at least one generator.
 11. The system as claimed in claim 10,wherein the electricity network or subnetwork is configured to supplyenergy from the at least one generator to a plurality of batteries via aplurality of wireless couplers, and the controller of the electricitynetwork or subnetwork configured to control the load on the at least onegenerator by varying the inductive power transfer to the plurality ofbatteries.
 12. The system as claimed in claim 10, wherein the at leastone generator comprises a renewable energy source selected from thegroup consisting of wind, solar and tidal energy.
 13. The system asclaimed in claim 6, wherein the system further comprises at least oneinductive power transfer pad comprising: two or more permeable magneticmaterial slabs arranged in a first layer; a coil having at least oneturn of a conductor, the coil being arranged in a second layersubstantially parallel to that of said slabs; and a shield membercomprising a backplate defining a third layer substantially parallel tothat of said slabs, said backplate arranged to direct magnetic fluxgenerated by said coil substantially perpendicular to the backplate;and/or at least one apparatus for charging comprising: a first couplerconfigured to selectively couple the battery to a high power electricalsupply; and a second coupler configured to selectively couple thebattery to a lower power electrical supply, wherein the second couplercomprises a pickup pad electrically coupled to the battery, whereinpower is transferred between the pickup pad and a charging pad byinductive power transfer.
 14. The system as claimed in claim 11, whereinthe system comprises a communication channel, and the controller isconfigured to control the plurality of wireless couplers by controlsignals communicated via the communication channel.
 15. A wirelesscharging pad comprising a slab of magnetic material arranged in a firstlayer, a coil, having at least one turn of a conductor, arranged on themagnetic material in a second layer that is substantially parallel tothe first layer, and electronics that control the power made availablefrom the coil for wireless power transfer, wherein the electronics areconfigured to receive a control signal from an electricity network orsubnetwork that is supplying mains electricity to the wireless chargingpad, and modulate the power made available for wireless power transferresponse to the received control signal.
 16. The wireless charging padof claim 15, wherein the wireless charging pad comprises acommunications channel, and the electronics are is configured to receivethe control signal from the electricity network or subnetwork via thecommunications channel.
 17. The wireless charging pad of claim 15,wherein the wireless charging pad comprises a single phase home-basedwireless charging pad.
 18. The wireless charging pad of claim 17,wherein the wireless charging pad has a transfer rating between 0.5 kWand 2.5 kW.
 19. The wireless charging pad of claim 15, wherein theelectronics are configured to derive the control signal from the mainselectricity received from electricity network or subnetwork.
 20. Thewireless charging pad of claim 15, wherein the electronics areconfigured to vary the power made available from the wireless chargingpad over a range between zero and full rated power, in increments of atleast 10%, responsive to the control signal.